line identity and regression suites

[John Yates]

In a conversation about improvement to our development processes
I expressed a wish for an index that mapped locations within the
codebase to applicable tests in the regression suite.  At present
I am unaware of any system that provides such a mapping.

But that got me to wondering whether the notion of line identity
over time in bzr might be made sufficiently concrete to make such
a system plausible.  Here is what I imagine.

Periodically we run the entire regression suite collecting code
coverage by individual test.  For the current tree under test today
this exercise would give me a mapping from file and line to a set
of applicable tests.

The problem is that if that mapping is recorded as file path and
line number then it is very fragile.  It will gradually decay as
simple edits are applied.  Code shuffling and/or tree rearrangement
will lead to much more rapid decay.  By contrast, if bzr can expose
a reasonably stable notion of line identity then the mapping could
be based on inventory-id and line-id.  This mapping would be fairly
robust in the face of intra-file edit and tree rearrangements.

Reactions?

/john

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John S. Yates, Jr.   508 665-6897 (voice)
Netezza Inc          508 665-6811 (fax)
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